It is the twenty-eighth (and twenty-ninth) digit in π. (3.141592653589793238462643383279...). If you start counting with 0 it is considered one of few Self-Locating strings in pi.
27 contains the decimal digits 2 and 7, and is the result of adding together the integers from 2 to 7 (2 + 3 + 4 + 5 + 6 + 7 = 27)
The Saros number of the solar eclipse series which began on 1993 March and ended on 713 April. The duration of Saros series 27 was 1280.1 years, and it contained 72 solar eclipses. Further, the Saros number of the lunar eclipse series which began on 1944 July and ended on 411 January. The duration of Saros series 27 was 1532.5 years, and it contained 86 lunar eclipses.
Electronics
The type 27 vacuum tube (valve), a triode introduced in 1927, was the first tube mass-produced for commercial use to incorporate an indirectly heated cathode. This made it the first vacuum tube that could function as a detector in AC-powered radios. Prior to the introduction of the 27, home radios were powered by a set of three or more storage batteries with voltages of 3 volts to 135 volts.
Kim Sung-kyu, South Korean singer, his album name called "27".
"Weird Al" Yankovic thinks it's a funny number, and it shows up on at least one song in almost every album of his.
References
Three of the cube is zero (science-fiction story)
Other
The Minneapolis-based artist Deuce 7 (a.k.a. Deuce Seven, Twenty Seven, 27).
In sports
The number of outs in a regulation baseball game for each team at all adult levels, including professional play, is 27.
In auto racing, 27 and 28 were Ferrari Formula one numbers from 1981 to 1995 except in 1990 when reigning WC Alain Prost had the right to use #1 and drove for the team, Nigel Mansell used #2. Popular Canadian driver Gilles Villeneuve used the number on his final days in F1. Later it was adopted by his son Jacques Villeneuve to claim the 1995 CART World Series title, and Canadian IndyCar driver James Hinchcliffe. Jean Alesi, another popular Ferrari driver was the last one ever to use the number back in 1995, also winning the last F1 race with it (as of January 2016), the Canadian GP. Ayrton Senna won his second Formula One World Championship using the mystic number 27 in 1990 in a McLaren Honda, as mentioned, the only time Ferrari didn't use the number during that period. Australian Alan Jones also won the World Drivers Championship in 1980 using number 27 in his Williams.
As of 2014, Formula 1 drivers selected their career numbers. The # 27, was chosen and is owned by Nico Hülkenberg
The Toronto Maple Leafs have a policy of not retiring numbers unless the player honoured either died or suffered a career-ending incident while a member of the team. Other players whose numbers would otherwise be retired instead have their numbers enshrined by the team as "Honoured Numbers", which remain in circulation for future players. The number 27 is currently honoured for Frank Mahovlich and Darryl Sittler.
Abbé Faria's prisoner number in the book The Count of Monte Cristo
One of the anthropomorphic math symbols Lisa Simpson imagines talking to her in The Simpsons episode "Girls Just Want to Have Sums", which, instead of offering the expected pun-based aphorism, rather unhelpfully only says "twenty seven"
In Stephen King's novel "It", It returns every 27 years to Derry.